Ashless nitrogen-containing dispersant additives generally contain a long chain hydrocarbyl component chemically linked to a polar nitrogen-containing component. The long chain hydrocarbyl component is typically derived from a hydrocarbon polymer and the chemical link is typically a dicarboxylic acid, ester or anhydride group, incorporated into the hydrocarbon polymer by reacting the polymer with an unsaturated dicarboxylic compound. The dicarboxylic group is subsequently reacted with a polyamine to form the polar head group. In practice, the chemical link is most commonly a succinic group derived from maleic anhydride. These functionalized polymers (e.g., succinated polymers) have been prepared by reacting the hydrocarbon polymer, typically a conventional polyisobutene obtained from butene streams by cationic polymerization in the presence of an AlCl.sub.3 catalyst, with an unsaturated dicarboxylic compound (e.g., maleic anhydride) at elevated temperature in the presence of chlorine. Exemplary processes are described in U.S. Pat. No. 3,215,707, EP-A-382450 and GB-A-1440219. The functionalized polymers have also been prepared by using a two-step chloro process in which the polymer is chlorinated in the first step and the resulting chlorinated polyalkene is then reacted with the unsaturated dicarboxylic compound at elevated temperature. Such a process is described in U.S. Pat. No. 3,172,892. The functionalized polymers have also been prepared by the direct thermal reaction of the hydrocarbon polymer and the unsaturated dicarboxylic compound, often referred to in the art as the thermal ene process. The thermal ene process is described in, for example, U.S. Pat. Nos. 3,361,673 and 3,401,118.
In the chloro and thermal ene processes, the dicarboxylic compound undergoes addition with the hydrocarbon polymer at an olefinic double bond site in the polymer, wherein the addition reaction results in the isomerization, but not the elimination, of the original double bond. This residual double bond content in the functionalized polymer can be problematic, because it will typically be present in the nitrogen-containing dispersant product derived therefrom, wherein it is a potential site for oxidation and degradation of the dispersant particularly in high temperature applications, such as use in a passenger car motor oil. The residual unsaturation can be saturated by hydrogenation, but this of course requires an additional processing step at additional cost.
The residual double bond content also provides a site for further addition of dicarboxylic compound during the functionalization reaction step which can result in a product containing polyfunctionalized (e.g., poly-succinated) polymer chains. Products consisting predominantly to substantially of monofunctionalized polymers are often preferred for use in the preparation of ashless dispersants in order to avoid or minimize adverse interaction of the dispersant with other additives employed in the lubricating oil or fuel. For example, dispersants based upon monofunctionalized polymer can have the advantage of minimizing adverse interactions (e.g., gelation) with overbased detergents, which interactions are described in EP-A-208560.
It can be difficult to control the chloro and thermal processes to produce monofunctionalized polymer in high yields. The more active chloro processes can produce functionalized product in high yields, but, without careful monitoring and control of reaction parameters, the product can contain significant to major amounts of polyfunctionalized polymer. The chloro processes raise environmental concerns as well, because their products contain residual amounts of chlorine. The thermal ene process avoids the use of chlorine and generally results in monofunctionalized product, but maleic anhydride reacts poorly and in low yields under thermal conditions with less reactive polymers such as conventional polyisobutene which has a low content of reactive vinylidene unsaturation and correspondingly large amounts of the less reactive tri- and tetra-substituted double bonds. The use of more extreme conditions in the thermal ene reaction to increase yields typically leads to the formation of substantial amounts of tar and sediments. If more reactive polymers are employed in the thermal ene reaction, such as reactive polyisobutenes as described in U.S. Pat. Nos. 4,152,499 and 4,605,808 and ethylene .alpha.-olefin polymers prepared using metallocene catalysts such as those described in U.S. Pat. No. 4,668,834, the reaction becomes more facile with higher yields, but the addition of a second enophile to a monofunctionalized polymer also competes effectively with addition of a first enophile to an unfunctionalized polymer leading to polyfunctional systems.
An alternative to the thermal ene and chloro processes is Koch carbonylation as described in CA-A-2110871, wherein the polymer is reacted with carbon monoxide and water, alcohol or thiol in the presence of an acid catalyst to form a carboxylic acid, carboxylic ester or carboxylic thiol ester at the site of olefinic unsaturation in the polymer. Because the double bond is consumed in the Koch reaction, monofunctionalized polymers with saturated backbones can be obtained from polymers having only one olefinic bond. On the other hand, the Koch reaction typically results in attachment of the carboxylic group to the more hindered side of the double bond, so that the resulting functionalized polymer can have a substantial proportion of neo substituted carboxylic groups. These neocarboxylic groups tend to be chemically stable and difficult to react with nucleophilic compounds including polyamines.
WO-A-95/21904 describes the preparation of carboxylic acids and esters useful as fuel or lubricant additives by reacting polymers having at least 30 carbon atoms and at least one double bond with carbon monoxide and water or alcohol in the presence a Group 8 to 10 metal or metal compound, but does not disclose the preparation of carboxylic amides.
EP-A-148592 describes the preparation of carboxylic esters from polymers containing residual carbon--carbon double bonds using carbon monoxide and alcohol in the presence of a protonic acid and as catalyst (a) at least one of the metals palladium, rhodium, ruthenium, iridium in elemental or compound form, and (b) a copper compound, both in the presence and absence of oxygen. It is disclosed that the carboxylic ester groups can be further reacted, if desired, with for example amines. The conversion and selectivity of the process cannot be determined from the data in the '592 document, but WO-A-95/21904 discloses that the repetition of the experiments described therein result in a conversion to desired products of less than 10%.
It is clear from the foregoing discussion that the need exists for improved processes for preparing carboxylic amide-containing polymers for dispersant applications. More particularly, processes are needed for the facile production of carboxylic amide-containing polymers from polyamines and hydrocarbon polymers, the carboxylic amide-containing polymer substantially to wholly composed of saturated polymer chains containing one amide group.